1. Field of the Invention
The present invention relates to a capillary holding structure for an ultrasonic horn.
2. Prior Art
In a wire bonding apparatus, as universally known, an ultrasonic horn holds a capillary at one end thereof and is moved vertically and in the X and Y (or horizontal) directions so that a wire which passes through the capillary is connected between electrodes on semiconductor pellets and leads on lead frames.
Conventional structures for holding a capillary on ultrasonic horns are disclosed in, for instance, Japanese Patent Application Laid-Open (Kokai) Nos. H6-163648 and H6-283578. In these structures, a vertical split groove is formed in the tip end of the ultrasonic horn so that a capillary attachment hole has a bifurcated structure, and a screw is formed so as to be offset from the capillary attachment hole in a direction perpendicular to the direction of the split groove; and a capillary is held in the ultrasonic horn when a bolt on the screw is tightened and the split groove is bent.
Thus, the prior art capillary described above takes a split tightening structure; and the screw is offset from the capillary attachment hole, and the left and right portions of the ultrasonic horn (on both sides of the split groove) act as springs so as to hold the capillary in between. Accordingly, the holding of the capillary is not significantly stable. Moreover, the capillary is held by the bending of the split groove; in other words, the capillary is held at its side surfaces which are parallel to the direction of ultrasonic vibration (i.e., the axial direction of the ultrasonic horn); and holding of the capillary at its side surfaces, which are caused to vibrate in the direction of the ultrasonic waves, requires a large holding force.